1. Field of the Invention
This invention relates to a method for the immunochemical measurement of trace components and particularly to a method for the immunochemical measurement of trace components.
2. Development of the Invention
Radioimmunoassay (hereafter merely "RIA") is a method for the assay of a trace component utilizing a specific antigen-antibody reaction. The basic principles of RIA are as follows. The reaction of a substance labelled or marked with a radioactive isotope (RI) in a given amount and a substance having a specific binding afffinity thereto in a given amount results in a coupled product of both of these components, while a part of the labelled substance remains in an unbound or unreacted free state. The reaction proceeds based on the laws of mass action in general, and, therefore, when an unlabelled substance is added to the reaction system, binding with a limited amount of binding protein is decreased and a certain relationship (calibration curve) can be established therebetween. As a result, an amount of an unknown substance can be determined from the calibration curve if the bound substance and the labelled substance in the free state are separated and either one or both are measured with respect to the RI amount.
Due to the high sensitivity and the simplicity of RIA, RIA is particularly applicable to the measurement and inspection of trace amounts of proteins in blood and hormones. Details thereon are given in, e.g., Kumahara and Shizume, NEW RADIOIMMUNOASSAY, pages 3 to 10 (1977), published by Asakura Publishing Co., Ltd., Tokyo, KISO SEIKAGAKU JIKKENHO (Basic Biochemical Experiments) (6), subtitled "Biochemical Assay" (1967), published by Maruzen Co., Ltd., Tokyo, P. D. Boyer et al, The Enzyme, vols. 3, 4 and 5 (1971), published by Academic Press, New York, and METHODS IN ENZYMOLOGY, edited by Sidney P. Colowick et al, vols. I, II, III, V and VII, published by Academic Press, New York.
However, RIA is subject to several disadvantages due to the use of RI labelling substances (.sup.125 I, .sup.131 I, etc.) which must have high specific radioactivity to maintain immune activity and must be of high purity. For these reasons, RIA involves the danger of radiation exposure and it is necessary to use expensive and unstable labelling substances which cannot be used for extended periods of time. In addition, special installations, equipment and personnel qualified to deal with radiation are required. Finally, after RIA, disposal of radioactive waste material and the ensuing pollution problems are encountered.
Further, in the case that analysis of a plurality of trace components in blood is to be used for making a diagnosis of a disease or for determining the condition of a disease, it is difficult to measure all such components at the same time in the same reaction system per the RIA method. To detect plural components, a number of examinations equal to the number of components must be carried out individually for each component and, therefore, it is necessary to increase the volume of blood examined according to the number of components. Obviously, an increase in the volume of blood taken is undesirable for young children or the weak.
In short, it has been substantially impossible to simultaneously measure a plurality of trace components in the same reaction system without increasing the volume of blood taken because each component cannot be labelled by different substances per the RIA method.